The invention relates to an office chair having a seat and a back which can both be adjusted steplessly in their inclination in the same direction by operation of a lever acting through a gas cylinder.
The aim of chairs of this kind is to give support for the back of a person sitting on it in line with medical and ergonomic requirements. German Utility Model No. 7 331 431 describes a simple construction of an adjustable chair of this kind. The seat and the back of the chair described therein are rigidly interconnected. The horizontal axis of pivoting of the resulting unit extends centrally on the bottom of the seat surface because the axis of pivoting lies on the support column or pillar of the chair. Unfortunately, in this case the edge of the seat rises or falls quite considerably when the inclination or tilt of the chair is adjusted. The thighs of the sitter, which are borne by the front part of the seat, therefore also rise or fall considerably, with the result that the feet cease to be at the proper distance from the floor. The misadjustment must be corrected by a vertical adjustment of the seat, but vertical adjustability is not provided in the seat and would call for additional construction complications, quite apart form the extra problem that the sitter would have to make a simultaneous coordinated adjustment of seat height together with inclination.
An office chair disclosed by Swiss Patent Specification No. 524,982 helps to solve this problem. This chair forms the starting point for this invention. In this known chair the gas compression spring extends substantially parallel to the seat on the underside thereof, the axis of pivoting of the seat extending near the front edge thereof. The advantage of this feature is that the chair front edge makes little, if any vertical movement when the inclination of the seat and the chair back is adjusted. In this construction the gas compression spring is operated by way of a horizontally operable lever on the bottom of the seat. This is an unsatisfactory feature ergonomically. Also, it is impossible to rock in this chair--i.e., to carry on making the adjustment of the seat and chair back in the same direction, as previously referred to, for as long as required; for this purpose the lever which operates the gas compression spring would have to be pulled all the time--an impossibility. When the front part of the seat is loaded, the chair back of this construction remains in its original position despite operation of the gas spring.